1. Field of the Invention
The present invention relates to a color cathode-ray tube.
2. Description of the Related Art
When a color cathode-ray tube is operated, an electron beam strikes a shadow mask (color selection electrode), and the shadow mask and a frame holding the shadow mask expand thermally, whereby an aperture on the shadow mask moves slightly toward a circumferential edge of the shadow mask. Consequently, the relative position between the aperture and a phosphor surface formed on a panel is changed and causes color displacement on a screen. In order to correct the color displacement, a support mechanism for fixing the shadow mask to the panel generally is provided with a function of correcting a change in position of the aperture of the shadow mask.
As the support mechanism, a substantially V-shaped support mechanism has been used conventionally. During thermal expansion of the shadow mask and the like, a spring member of the substantially V-shaped support mechanism is deformed so that the shadow mask approaches the phosphor surface side. Therefore, color displacement attributable to a change in position of the aperture of the shadow mask can be prevented. Furthermore, there is no problem that the shadow mask is rotated, for example, as in the case of using an elongated plate-shaped spring composed of two kinds of metals called a bimetal spring.
However, the substantially V-shaped support mechanism is likely to be deformed or to come off a stud pin when an external impact attributable to dropping or the like is applied to a cathode-ray tube, compared with the bimetal spring. In order to solve this problem, an attempt has been made to improve the material for the spring member (e.g., see JP6(1994)-44916A).
Recently, in a color cathode-ray tube, a panel on which an image is to be displayed is flattened since the flat panel reduces the reflection of external light and enhances the appearance. Along with this, as a shadow mask having a function of color selection, the one welded to a frame under the application of tension has come into use in place of a press-type shadow mask. A shadow mask structure provided with such a so-called tension-type shadow mask has a large weight so as to maintain the mechanical strength required for withstanding a tensile strength. Thus, there is a problem that sufficient strength against an external impact cannot be ensured merely by improving the material for the spring member. In particular, when an external impact is applied in a direction parallel to a long side direction of a screen, the spring member is likely to be deformed plastically. When the spring member is deformed plastically, the relative position between the aperture of the shadow mask and the phosphor surface is changed and causes color displacement.